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(2018) 2، عدد 36مجلة وقاية النبات العربية، مجلد 164
Research Paper (Host Resistance: Fungi) (أمراض فطرية: مقاومة العائلبحـوث )
Slow rusting of bread wheat landraces to Puccinia striiformis f.sp. tritici
under artificial field inoculation
Fida Alo1,2, Walid Al-Saaid1, Michael Baum3, Hesham Alatwani4 and Ahmed Amri3
(1) Department of Plant Biology, Faculty of Science, University of Aleppo, Syria;
(2) Biodiversity and Integrated Gene Management Program (BIGMP), International Centre for Agricultural Research in the
Dry Areas (ICARDA), Egypt, email: [email protected]; (3) BIGMP, ICARDA, Morocco;
(4) General Commission for Scientific Agricultural Research (GCSAR), Syria
Abstract Alo, F., W. Al-Saaid, M. Baum, H. Alatwani and A. Amri. 2018. Slow rusting of bread wheat landraces to Puccinia
striiformis f.sp. tritici under artificial field inoculation. Arab Journal of Plant Protection, 36(2): 164-175. Yellow rust caused by Puccinia striiformis f. sp. tritici is the most devastating fungal disease of wheat, especially in the Central and
West Asia and North Africa (CWANA) region. Most of the released cultivars in CWANA have become susceptible to the new virulence Yr27.
Growing durable resistance cultivars is the most economical control measure. A field study was conducted to evaluate 500 bread wheat
landraces along with the susceptible control ‘Morocco’ using artificial inoculation under field conditions at Tel Hadia, Syria during 2010/11
and 2011/12 growing seasons. The most prevailing and spreading yellow rust virulence (70E214) was used for artificial inoculation. Disease
scoring started when disease severity was more than 50% on the leaves of cv. Morocco and continued for four readings at 7 days intervals.
Slow rusting resistance was assessed based on development of the disease over time using the area under disease progress curve (AUDPC),
coefficient of infection (CI), final rust severity (FRS), infection rate “r” and relative resistance index (RRI). None of the landraces showed
immune reaction and 10% showed the lowest values for all parameters, suggesting that major genes control resistance in these landraces.
Approximately 65% of the landraces were marked as having different levels of slow rusting and 25% were highly susceptible. Cluster analysis
based on partial resistance parameters of the landraces along with cv. Morocco revealed two major clusters: susceptible and low level of slow
rusting were grouped in the first cluster; resistant, high level and moderate level of partial resistance were grouped in the second cluster. These
groups were also confirmed using principal coordinate analysis. By comparing the results of RRI and others parameters, it appeared that
landraces with very low values exhibited high RRI value of 9, while those that showed high, moderate, and low levels of slow rusting, had
RRI ranges of 8-9, 7-8 and 5-7, respectively. Landraces with maximum values from each parameter showed very low RRI values of less than
5. The results also suggest that AUDPC, CI, and FRS are the more appropriate parameters for assessing slow rusting than infection rate.
Correlation coefficient and principle component analysis revealed a high and positive correlation between these parameters.
Keywords: Disease resistance, yellow rust, bread wheat, landraces.
Introduction1
Wheat is the second most important food crop in the
developing world after rice, with annual production of 720
million tons (FAO, 2014). Higher and sustainable production
is needed to meet the demand of the world increasing
population.
Wheat production is severely affected by many abiotic
and biotic stresses (Chen et al., 2013). The development of
new tolerant and resistant varieties, is the more efficient
approach to ensure sustainable wheat production.
Among the major wheat diseases, yellow rust caused
by P. striiformis f. sp. tritici appears the most devastating
worldwide after breakdown of the resistance of most released
varieties (Hovmoller, 2001). In recent years, significant yield
losses were reported in CWANA region and beyond after the
appearance of virulence against Yr27 gene (Solh et al.,
2012).
The use of fungicides to control yellow rust is not
economical as it significantly increases the costs of
production discouraging its use by small farmers. In addition,
the excessive use of pesticides is not friendly to environment,
and the adoption of an integrated disease management
http://dx.doi.org/10.22268/AJPP-036.2.164175
© 2018 Arab Society for Plant Protection الجمعية العربية لوقاية النبات
approach based on use of genetic resistance (Chen, 2005;
Singh et al., 2005) is becoming more desirable.
Slow rusting or horizontal resistance or partial
resistance is a form of quantitative resistance that can slow
the incidence and development of yellow rust in the field
(Wang et al., 2000). It is mainly controlled by minor genes
having a different mode of action and do not provide
immunity (Herrera-Fossel et al., 2007). Therefore, continued
access to new sources of resistance in genetic resources is
needed (Bux et al., 2011). In this regard, evaluation of gene
bank accessions and other germplasm is a key in this
direction.
Slow rusting could be assessed through different
measures such as the final rust severity (FRS) (Parlevliet &
Ommeren, 1975), area under diseases progress curve
(AUDPC) (Wilcoxson et al., 1975), infection rate “r” (Broers
et al., 1996), coefficient of infection (CI) (Pathan & Park,
2006), and some researchers used relative resistance index
(RRI) (Akhtar et al., 2002). Slow rusting has been assessed
using only CI and some researchers consider it as the most
commonly used parameter for assessment of yellow rust
reaction (Ali et al., 2009). Other researchers used AUDPC,
“r” and final disease severity to assess slow rusting (Ali et
al., 2007). Some scientists use RRI and CI to assess partial
165 Arab J. Pl. Prot. Vol. 36, No. 2 (2018)
resistance to yellow rust in wheat (Afzal et al., 2009;
Mahmoud et al., 2015).
The present study is designed to evaluate a set of 500
bread wheat landraces for slow rusting resistance and to test
the efficiency of different slow rusting epidemiological
parameters, and assess the relationship among them.
Materials and Methods
This study was carried out during two seasons 2010/11 and
2011/12 at International Center for Agricultural Research in
the Dry Areas (ICARDA) Tel Hadya experiment station,
located in Northern Syria at 36° 16‘N, 36° 56‘E, altitude 284
m.a.s.l. with long-term average annual rainfall of 350 mm
(Ryan et al., 1997).
Plant materials and germplasm sources
A subset of 500 bread wheat landraces collected mainly from
CWANA region, were obtained from ICARDA gene bank.
The landraces originated from 10 countries (314 accessions
from Iran, 98 from Afghanistan, 24 from Syria, 21 from Iraq,
19 from Pakistan, 10 from Egypt and 6 from Morocco). The
remaining eight landraces belong to China (6), Russia (1) and
Eritrea (1).
Planting the experiment and disease assessment
During 2010/2011 season, the 500 landraces were grown in
one-meter length plot, and subject to artificial inoculation
using the race (70E214). The susceptible check “Morocco”
was used as disease spreader and planted around the
experiment and as susceptible check after each 10
accessions. The disease severity was recorded twice during
the season.
During 2011/2012 season, the seeds of selected single
heads from each accession along with the susceptible
spreader row check variety “Morocco” were planted under
irrigated conditions and were subject to artificial inoculation
using the same race (70E214). Artificial inoculation was
done following the procedure described by (Roelfs et al.,
1992) in both seasons. Only 417 accessions originating from the 500 original
landraces were assessed for slow rusting using different
parameters: disease severity (DS), final rust severity (FRS),
and area under disease progress curve (AUDPC), coefficient
of infection (CI), Infection rate (r) and Relative Resistance
Index (RRI).
Scoring of the disease severity (%) on each landrace
started when the susceptible check reached to 50% severity,
then observations were taken at 7 days interval on 9th April,
16th April, 23rd April, and 1st May 2012. Disease severities
were measured according to the Modified Cobb scale
(Peterson et al., 1948).
The coefficient of infection (CI) was calculated by
multiplying final disease severity (DS) by constant values
(the numerical notation for the host response) of infection
type (IT) in as suggested by (Pathan & Park, 2006).
The area under the disease progress curve (AUDPC),
was calculated using the software obtained from CIMMYT
(Joshi & Chand, 2002). The equation used is given as:
𝑨𝑼𝑫𝑷𝑪 = ∑{[𝒀𝒊 + 𝒀(𝒊+𝟏)
𝒂
𝒊=𝟏
]/𝟐 } × [𝒕(𝒊+𝟏) − 𝒕𝒊]
Where, a = total number of observations. 𝑡𝑖. =day i (time)
expressed as number of days after sowing, t (i + 1) – 𝑡𝑖. =
Time (days) between two disease observation dates and 𝑌𝑖 =
Number of pustules at time 𝑡𝑖.
The infection rate “r”, which represents the unit leaf
area occupied by disease per day, was estimated for the
whole epidemic period after the time when “Morocco”
showed more than 50% severity, following (van der Plank,
1968). The relative infection rate was worked out for each
accession by comparing its “r” value with that of the
susceptible check.
The Relative Resistance Index (RRI) was calculated,
using a 0 to 9 scale, where 0 represents the most susceptible
and 9 the highly resistant accessions. The highest average
coefficient of infection (ACI) of an accession is set at 100
and all other accessions are adjusted accordingly. This gives
the Country Average Relative Percentage Attack (CARPA).
The standard for desirable index was maintained at ≤7
whereas the value for acceptable index was fixed as 5
(Aslam, 1982). The following formula was used for
calculating RRI (Akhtar et al., 2002):
RRI =(100 − 𝐶𝐴𝑅𝑃𝐴)
100× 9
Statistical analysis Cluster analysis and principal coordinate analysis
(PCoA)
Euclidian distance between landraces was calculated from
the standardized data matrix to assess the genetic distance,
hierarchical cluster was made by un weighted pair-group
average method using arithmetic averages (UPGMA), using
DAR win 6 software (Perrier & Jacquemoud-Collet, 2006).
The same data matrix was also used to undertake a Principal
coordinate analysis (PCoA) with the same software in order
to obtain a graphical representation of the genetic diversity
patterns for differentiating the landraces.
Principle competent analysis (PCA)
For PCA analysis, the function PRCOMP was used from the
STATS package in R (R Core Team, 2016) and 3D view of
the PCA was drawn using an in house R script. The
correlation coefficient between any two traits is
approximated by the cosine of the angle between their
vectors (Yan & Rajcan, 2002). On this premise, two traits are
positively correlated if the angle between their vectors is an
acute angle (< 90°) while they are negatively correlated if
their vectors are an obtuse angle (> 90°), and right angles in
case of no correlation. A short vector may indicate that the
trait is not related to other traits (Yan & Kang, 2003).
Results
During season 2010/2011, there was a good development of
yellow rust and the spreader susceptible check scored 70S to
100S. The 500 landraces showed different reactions to the
disease and based on FRS there are 246 S, 48 MSS, 12 MS,
19 MRMS, 5 MR, 29 RMR and 141R (Figure 1).
(2018) 2، عدد 36مجلة وقاية النبات العربية، مجلد 166
Figure 1. Number of bread wheat landraces for each yellow rust infection type.
Disease severity (DS) value
A high disease pressure was observed in 2011/12 season as
revealed by the susceptible check “Morocco” which
exhibited 100S in all the plots, while the mean level of YR
severity ranged from 5R (HR) to 100S (HS) for the tested
landraces. The landraces were divided into seven groups
depending on infection type: 73 landraces (18%) were
resistant (R), 75 (18%) were resistant to moderately resistant
(RMR), 30 landraces (7%) were moderately resistant (MR),
60 landraces (14%) marked as moderately resistant to
moderately susceptible (MRMS), 32 landraces (8%) were
moderately susceptible (MS), 22 landraces (5%) were
moderately susceptible to susceptible (MSS), and 125
landraces (30%) were susceptible to high susceptible (S).
The disease development over time is presented in
Figure 2, depending on the four reading dates assessment and
the corresponding severity for each infection type (the
landraces were grouped according to their infection type and
the value of disease severity for each reading date was
calculated, so each landrace in each infection type was
represented by four reading dates). Morocco showed high
levels of disease severity and almost linear pattern of
increase between initial and final scorings. Most of
susceptible landraces were having more increase in severity
between second and final score, and some of them were very
close to the susceptible check at final score. Almost all
landraces that belong to infection type R showed the lowest
levels of severity over the four scoring dates.
The curve showed slow progress of the disease for
landraces showing, MR and/or MS and MSS infection types.
These results were in accordance with all studies that showed
that varieties rated as MR or MRMS or MS and MSS
generally exhibit slow rusting.
The quantitative resistance (race-nonspecific) usually
behave in a stable manner compared to the race-specific
resistance, because of that, the selection for quantitative
resistance is expected to be more durable. To assess the slow
rusting, bread wheat landraces were grouped in to three main
categories of slow rusting (low, medium and high) based on
the results from different slow rusting parameters, in addition
to the susceptible group and the race-specific resistant group
Race-specific resistant group
None of the bread wheat landraces were recorded as
resistant, however 39 landraces with scores of 5R, 10R, 20R
showed the lowest values of different slow rusting
parameters (FRS <20, AUDPC value less than 50, CI value
less than 3, and r-value less than 10, and RRI the value was
9). This group is believed to have race-specific resistance,
and may carry a single or combination of major genes of
resistance.
According to the landraces origin, the accessions from
Iran (which representing the highest number of accessions in
this study) had the biggest number with 22 resistant
landraces, 6 from Afghanistan, 4 from Iraq and 3 from Syria
and Pakistan, and one form Morocco.
Slow rusting groups
The landraces with slow rusting were divided into three
groups based on the slow-rusting parameters, Group 1: The
landraces in this group have low level of FRS value of (0-
30), AUDPC value ≤200, CI value were (0-20) and with r-
value less and equal to 30, and are marked as having high
level of slow rusting. Different numbers of landraces in each
category for different parameters were detected. A total of 51
landraces showed high level of partial resistance with FRS
value less than 30,128 landraces had CI≤ 20,126 with
AUDPC≤200and121 with r ≤30. Group 2: The landraces in
this group showed low level of FRS value of (31-50) (104
landraces), CI value (21-40) (65 landraces), AUDPC value
(201-500) (69 landraces), and with “r” value (31-50) (35
landraces), and are marked as having a moderate level of
slow rusting resistance. This group showed moderate level
of severity and moderately resistant to moderately
susceptible reaction type. Group 3: The landraces in this
group had high level of slow rusting parameters and were
141
29
519 12
48
246
286 1 4 2 10
49
R RMR MR MRMS MS MSS S
-50
0
50
100
150
200
250
300
Infection typeNumber of Landraces %
167 Arab J. Pl. Prot. Vol. 36, No. 2 (2018)
characterized as having low level of slow rusting. This group
showed high levels of disease severity and moderately
susceptible to susceptible reaction, with FRS value (51-70),
CI value (41-60), AUDPC value ranging between (501 and
900) and with r-value range of (51-90).
A total of 73 landraces were classified in this category
based on FRS parameter, 43 landraces based on CI, 74
landraces based on AUDPC values, and 56 landraces based
on r-value.
Susceptible group
This group showed high level of severity and susceptibility
(80S to 100S) and had greater values for all slow-rusting
parameters than the other groups, and includes the
susceptible check “Morocco”. Based on the parameters, 150
landraces had FRS>70, 142 landraces had CI value of more
than 60, 109 landraces with AUDPC value exceeding 900,
and 166 landraces had r-value higher than 90. According to
the landraces origin, 73 accessions belongs to Iran, 19 from
Afghanistan, 5 from Iraq and 5 from Syria.
A
B
C
Figure 2. Yellow rust progress curves on bread wheat landraces obtained by plotting disease severity (DS) against the number
of days after sowing. (A) Yellow rust progress curves of R-RMR. (B) Yellow rust progress curves of MR-MRMS-MS-MSS. (C)
Yellow rust progress curves of S.
0
20
40
60
80
100
120
4/2/2012 4/9/2012 4/16/2012 4/23/2012 5/1/2012
R-RMR
Morocco check
0
20
40
60
80
100
120
4/2/2012 4/9/2012 4/16/2012 4/23/2012 5/1/2012
MR-MRMS-MS-MSS
Morocco check
0
20
40
60
80
100
120
4/2/2012 4/9/2012 4/16/2012 4/23/2012 5/1/2012
S
Morocco check
(2018) 2، عدد 36مجلة وقاية النبات العربية، مجلد 168
Relative Resistance Index (RRI)
The relative resistance index RRI was determined using the
obtained data from both seasons, after calculating the ACI.
Based on RRI values, out of 417 landraces, 90 landraces had
highest RRI value of 9, 143 exhibited RRI value ≥7<9 and
all were within the desirable range for adequate resistance to
yellow rust. Another 75 landraces were included among the
acceptable range of resistance having RRI value ≥5<7, but
107 landraces showed RRI value of less than 5 and placed
under undesirable range. Only two landraces collected from
Afghanistan showed RRI value of 0 like Morocco.
By comparing the results obtained from RRI and others
parameters we found out that landraces with infection type
(R-MR) and with very low values for all parameters,
exhibited RRI values of 9, while those that showed high, and
moderate and low levels of partial resistance had RRI value
ranges of between 8-9, 7-8 and 5-7, respectively. The
landraces that have susceptible infection type S and
maximum values for each parameter showed very low value
of RRI<5.
Association between slow rusting parameters
Field assessment for partial resistance was evaluated through
FRS, AUDPC, CI and r-value. The results suggested that the
landraces which are characterized as having slow disease
development (low AUDPC, FRS, CI and “r”) could be
considered as having partial resistance to yellow rust.
In the present study, an attempt was made to elucidate
the relationships between these parameters by using
Pearson’s correlation coefficients. High and significant
positive correlations were found among all disease
assessment parameters (Figure 4). The highest correlation
coefficient was between AUDPC and CI (r = 0.99), and the
lowest value was between “r” and AUDPC (r =0.86).
However, all measured parameters seem to be good
estimators of partial resistance to yellow rust in wheat (Table
1).
Table 1. Correlation coefficients between yellow rust slow
parameters in bread wheat landraces.
AUDPC
CI FRS r-value
AUDPC —
CI 0.99 —
FRS 0.86 0.90 —
“r” 0.74 0.77 0.94 —
FRS: Final Rust Severity, AUDPC: Area under Disease Progress
Curve, r-value:
Infection Rate, ACI: Average coefficient of Infection, RRI:
Relative resistance Index
Principal component analysis (PCA)
Biplot analysis using Principal Component Analysis is used
to show graphically the relationships between all partial
resistance parameters including RRI. The first two PCAs
accounted for about 99.2% of total variation. The most
prominent relations are shown in Figure (4). Significant and
positive correlations were found between ACI and AUDPC;
between FRS and “r”, as indicated by the small obtuse angles
between their vectors. Good and positive correlations were
also confirmed between AUCPC, ACI and FRS. There was
a near zero correlation between AUDPC and “r”, between
ACI and “r”, as indicated by the near perpendicular vectors.
There were negative correlations between AUDPC and RRI,
and between ACI and RRI, as indicated by the angle of
approximately 180 degrees.
Diversity analysis
Cluster analysis
Cluster analysis based on partial resistance parameters
of bread wheat landraces along with Morocco, revealed two
major clusters. Susceptible and low level of slow rusting
landraces was grouped in the first cluster. Resistant, high
level and moderate level of partial resistance were grouped
in the second cluster (Figure 5). The first cluster included one
sub-cluster with Morocco and two landraces from
Afghanistan with maximum distance from all the other
landraces and having the highest values of all parameters and
“0” value of RRI. The other sub-cluster include landraces in
two groups: The first group consist of all landraces marked
as susceptible, and the second group included two sub-
groups one of them having low level of partial resistance and
the second as moderate to low level of partial resistance, with
infection type (MS-S).
The second cluster comprises landraces having better
level of slow rusting. This cluster is divided into two main
sub-clusters, the first one includes moderate level of partial
resistance, and the second sub-cluster consist of two groups:
the first group has two different sub-groups, one consisting
of landraces with lowest values of all parameters and “9”
value of RRI, which could carry a major gene or a
combination of major genes for resistance to yellow rust. The
second sub-group includes landraces with high level of
partial resistance, with low values of all parameters and “9”
value of RRI.
The second group comprised also two sub-groups: the
first one consists of landraces marked as having high level of
partial resistance and “8” for RRI parameter, and the last sub-
group consisted of landraces scored as high to moderate level
of partial resistance. The landraces in this sub-group are
classified as having moderate to high levels of partial
resistance and infection type (MR-MS).
Principal coordinates analysis (PCoA)
Principal coordinates analysis (PCoA) has been performed
for a clear separation among the groups having different
levels of resistance (Figure 6). In accordance with the
dendrogram, the first two components explained 99.5% of
the total variation. The first principal coordinate clearly
separated the landraces having susceptible and low level of
partial resistance on the left side of the diagram and the
landraces with better level of partial resistance and resistance
clustered on the right side.
169 Arab J. Pl. Prot. Vol. 36, No. 2 (2018)
A
B
C
D
E
F
Figure 3. Associations between different yellow rust parameters used to assess partial resistance to yellow rust in bread wheat:
(A) “r” with CI. (B) “r” with AUDPC. (C) “r” with FRS. (D) FRS with AUDPC. (E) CI with FRS. (F) CI with AUDPC.
y = 2.5029x + 14.603
R² = 0.7722
-40
10
60
110
160
210
260
0 50 100
"r"
CI
y = -9E-05x2 + 0.236x
R² = 0.7456
-50
0
50
100
150
200
250
0 500 1000 1500 2000
"r"
AUDPC
y = 1.7001x + 0.3065
R² = 0.9453
-50
0
50
100
150
200
250
0 50 100 150
"r"
FRS
y = 0.0661x + 9.0272
R² = 0.8625
0
20
40
60
80
100
0 500 1000 1500 2000
FR
S
AUDPC
y = 0.5855x - 1.5335
R² = 0.9097
-10
0
10
20
30
40
50
60
70
80
90
0 50 100 150
CI
FRS
y = 0.0436x + 0.7332
R² = 0.9973
0
10
20
30
40
50
60
70
80
90
0 500 1000 1500 2000
CI
AUDPC
(2018) 2، عدد 36مجلة وقاية النبات العربية، مجلد 170
Figure 4. Correlations between slow rusting parameters using Principal component analysis (PCA)
Figure 5. The dendrogram of landraces generated from UPGMA using Neighbor-joining analysis
171 Arab J. Pl. Prot. Vol. 36, No. 2 (2018)
Figure 6. Factorial coordinate analysis for bread wheat landraces as generated by DARwin Software using dissimilarity
coefficient matrix calculated from all partial resistance parameters.
Discussion
Improving resistance to yellow rust has become an important
target for bread wheat breeding programs at ICARDA and
around the world, after most of the varieties grown by the
farmers as well as most elite germplasms have become
susceptible to the new virulence (70E214). During both
seasons, epidemics of yellow rust are widely spread in
CWANA countries after the wide spread of (70E214)
virulent populations. The climatic conditions during 2010-
2012 seasons were favorable for the development of the
disease and the success of artificial inoculation with
(70E214) virulent population. The high susceptibility of
Morocco used as spreader row showed the uniformity of
inoculation, which has allowed effective screening of the
accessions, planted, including good assessment of slow
rusting resistance. The focus of this study was on
identification of genetic sources with slow rusting resistance
in bread wheat accessions.
The evaluated accessions exhibited a wide range of
reaction to yellow rust ranging from high susceptible to
highly resistant and most of the entries showed better
resistance than Morocco. Most of the accessions were more
resistance under high disease pressure as compared to the
susceptible check. Similar diversity in reaction to yellow rust
is found by other researchers for other sets of germplasm
showing the possibility of finding new sources of resistance
to emerging virulence’s (Ali et al., 2009; Sthapit et al.,
2014).
Field-based assessment of partial resistance is essential
for the development of new varieties with long lasting
resistance. Different parameters, FRS, AUDPA, CI, “r” were
used in this study to assess the slow rusting in bread wheat
landraces along with RRI. These parameters showed large
ranges which have allowed classifying the landraces into five
groups: one group with potentially vertical resistance, one
group with susceptible reaction and three groups with low,
medium and high slow rusting reactions.
None of the tested landraces showed resistant reaction
and some landraces showed even higher susceptibility than
Morocco which used frequently around the world as rust
spreader. The group with race-specific type of resistance
included 39 landraces (10%) traced to different geographic
areas and their resistance is controlled by major genes. Other
researchers reported, that the lines having resistant reaction
at adult plant stage and low value of slow rusting parameters
may carry major genes along with minor genes of resistance,
and the accessions with CI up to 5% are probably carrying
major genes (Ali et al., 2009; Safavi et al., 2010). The
duration of the effectiveness of major genes is often limited
by the selection of new virulent races as reported by many
authors (Safavi et al., 2010; Chen et al., 1993; Wan & Chen,
2012). The protection using this type of resistance can be
extended through either using the different genes
sequentially or through their pyramiding and within an
integrated disease management approach. These findings
confirm the value of genetic resources held ex situ in gene
banks to continuously supply needed diversity to overcome
major challenges including the new virulence’s for major
diseases such as yellow rust. This study has shown the
existence of large number of accessions with partial
resistance which could be used within the strategy for more
durable protection against the disease, as it is believed to be
race non-specific, Approximately (55-65%) of the tested
landraces showing infection types (R-MR, MR, MR-MS,
MS, and MS-S) can be classified into different levels of slow
rusting as the rust development was slower and the spores
were surrounded by necrosis and chlorosis. Landraces with
slow rusting mechanism of resistance are expected to possess
(2018) 2، عدد 36مجلة وقاية النبات العربية، مجلد 172
several genes that confer partial and durable resistance
(Dehghani & Moghaddam, 2004; Tabassum, 2011) or could
be combined to provide near resistance (Angus & Fenwick,
2008).
According to all used partial resistance parameters,
landraces with slow rusting were divided into three groups
with high, moderate, and low slow rusting, with the infection
types MR, MS and MSS. These results were in accordance
with (Brown et al., 2001) and (Singh et al., 2005), who
mentioned that the cultivars with MS or MR infection type
may carry durable resistance genes. Several parameters were
used to assess the slow rusting type of resistance.
Landraces with CI values of 0-20, 21-40, 41-60 were
regarded as possessing high, moderate, and low levels of
slow rusting (Ali et al., 2007; Pathan & Park, 2006). Safavi
et al. (2010) used the same parameters to classify wheat
germplasm into groups with low to high levels of slow
rusting and classified the accessions that showed CI value
greater than 60 as susceptible. Although values of (61–80)
with (MS-MSS) infection type could reflect the presence of
minor genes. CI values within this range may have also
resulted from variation in environment and/or growth stage
at the time of scoring.
Considering high disease pressure maximum FRS
(100%) was recorded for Morocco and 98 landraces showed
FRS 90-100%. Depending on this parameter, the tested
landraces were divided in to three groups of partial
resistance, i. e., high, moderate, low levels of partial
resistance having 1-30%, 31-50%, and 51-70% FRS,
respectively. This parameter is also used for assessment of
slow rusting by other authors (Herrera-Fossel et al., 2007;
Safavi et al., 2010).
Landraces were also categorized into three groups of
partial resistance using AUDPC. This parameter is the most
widely used to assess disease development and slow rust (Ali
et al., 2008; Broers et al., 1996; Bux et al., 2012); other
studies (Mahmoud et al., 2015; Saleem et al., 2015)
classified cultivars with AUDPC of less than 300 as having
high level of slow rusting.
The infection rate “r” seemed not a reliable estimate of
slow rusting resistance compared to FRS, ACI, and AUDPC,
due to its estimation depends on the linear regression of
disease severity across the four readings. During the period
of reading, 164 landraces showed disease development and
"r" values superior to the check, although the actual infection
rate for “Morocco” may even be more. Some landraces
showed even negative r-values, because they showed MS
infection type at the early stage and R to MR infection types
at the advanced stages, indicating that the rate of disease
development didn’t change with the host developmental
stages. Indeed, it is possible the growth rate will be negative
while the disease is increasing, if the host grows faster than
the pathogen (Kushalappa & Ludwig, 1982). In other words,
the value of this parameter does not reflect the final infection
type of the studied landrace, but only the degree of disease
development during the time of the study. Similar results and
justifications were also reported for yellow rust on 20 wheat-
breeding lines in Pakistan (Ali et al., 2007).
Overall, AUDPC and CI showed high and positive
correlation that was confirmed using principal component
analysis. Similar relationships among the two parameters
were found by other researchers (Safavi et al., 2010;
Sandoval-Islas et al., 2007). Field selection of partial
resistance trait preferably using low AUDPC and terminal
rating CI is feasible in situations, where greenhouse facilities
are inadequate (Singh et al., 2007). In the present study a
high correlation (0.99) was found between FRS and AUDPC
which is consistent with previous studies made on yellow
rust of wheat by (Safavi, 2015; Tabassum, 2011) in Pakistan.
Since AUDPC, CI and FRS parameters are strongly
and positively correlated, they can then be used
interchangeably to assess slow rusting, as also suggested by
other researchers (Safavi et al., 2010; Safavi & Afsari, 2012;
Sandoval-Islas et al., 2007).
However, FRS and CI are requiring less labor and time
for recording in contrast with AUDPC and infection rate, as
also reported by (Safavi et al., 2013). Other studies also
privileged FRS as a parameter to measure the resistance
levels over other slow rusting parameters (Tabassum, 2011;
Taye et al., 2014), FRS is assumed to represent the
cumulative result of all resistance factors during the progress
of epidemics (Parlevliet & Ommeren, 1975). Ali et al. (2008)
recommended the use of CI to assess slow rusting.
In wheat breeding program, lines are tested over
several years and locations and the use of the Relative
Resistance Index (RRI) could be more appropriate in
assessing partial resistance. Similarly, many researchers
defined the desirable and acceptable values of RRI between
7 and 5, respectively to determine germplasm with partial
resistance (Afzal et al., 2009; Akhtar et al., 2002). Most
recently, Mahmoud et al. (2015) used the RRI parameter
along with CI to identify wheat genotypes resistant to yellow
rust in (RILs) derived from a cross between two Egyptian
landraces.
Partial resistance is desired by plant breeders to combat
the fast evolving diseases such as rusts. Based on AUDPA,
FRS and CI along with RRI, 250 landraces out of 417
landraces, were supposed to be having varying degree of
slow rusting. However, these landraces should be tested at
seedling growth stage in the greenhouse to confirm the
presence of major genes.
These findings confirm the value of genetic resources
held ex situ in gene banks to continuously supply breeding
programs around the world with needed diversity to
overcome major challenges including the new virulence’s for
major diseases such as yellow rust. The high number of
sources of resistance and their geographic spread could
reflect the diversity of genes controlling resistance to yellow
rust. Slow rusting and adult plant resistance is highly needed
to cope with the rapidly evolving and expanding virulence’s
of yellow rust.
173 Arab J. Pl. Prot. Vol. 36, No. 2 (2018)
الملخص يسببه الذي األصفر . المقاومة البطيئة لمدخالت القمح الطري للصدأ2018وليد السعيد، مايكل بوم، هشام العطواني وأحمد عمري. عالو، فدا،
.175-164(: 2)36ة النبات العربية، صطناعية. مجلة وقاياإلتحت ظروف العدوى الحقلية Puccinia striiformis f.sp. tritici فطرال
خاصة في منطقة وسط شرق آسيا وشمال وبللقمح من األمراض الفطرية األكثر تدميرا Puccinia striiformis f.sp. triticiالصدأ األصفر الذي يسببه فطر يعدزراعة األصناف ذات المقاومة . ولذلك فإن Yr27لسالللة الجديدة با قابلة لإلصابة، حيث أصبحت معظم األصناف التي تم تطويرها في هذه المنطقة /CWANAفريقيا أ
" في ظل Morocco" القابل لإلصابةمن القمح الطري مع الصنف ا محلي ا صنف 500يم و لتقق اإلقتصادية الناجحة. أجريت دراسة حقلية ائالبطيئة هي من أكثر الطر اإلعداءإلجراء (70E214) سالالت الصدأ األكثر انتشارا ، وتم استخدام 2011/2012و 2010/2011خالل الموسمين ةسوريحديا، الظروف الحقلية في تل
%، حيث تم أخذ أربع قراءات بفاصل سبعة أيام بين كل 50أكثر من Moroccoأخذت القراءات عندما كانت شدة اإلصابة على أوراق نبات الشاهد االصطناعي. (، معامل العدوى AUDPCقت باستخدام معامل المساحة تحت منحنى تطور المرض )مقاومة الصدأ البطيئة على أساس تطور المرض مع مرور الو مت و ق. تينءقرا
(CI) شدة اإلصابة النهائية ،final rust severity (FRS) معدل اإلصابة ،infection rate “r” ( و معامل المقاومة النسبيةRRI )Ralative Resistnce Index لم .، وهذا ما يدعو لإلعتقاد بوجود مورث رئيس صغيرة للمؤشرين السابقين ا ناف قيممن األص %10جدا ، بينما أظهرت فعل مقاوم يظهر أي من األصناف المقاومة ردكانت حساسة جدا . وباالعتماد %25مختلفة من المقاومة البطيئة و من األصناف مستويات %65ألصناف المحلية. وامتلك حوالي مسؤول عن صفة المقاومة في هذه ا
مع األصناف القابلة لإلصابةوالتي أظهرت وجود مجموعتين رئيسيتين: األصناف Moroccoعلى نتائج المؤشرات السابقة تم انشاء شجرة القرابة لألصناف مع الصنف ذات المستوى العالي والمتوسط من المقاومة البطيئة في المجموعة ذات مستوى منخفض من المقاومة البطيئة في المجموعة األولى، واألصناف المقاومة واألصناف
مع نتائج المؤشرات األخرى، تبين أن RRI، وبمقارنة نتائج مؤشر المقاومة النسبية PCA تحليل العناصر )المكونات األساسية(الثانية. وتم تأكيد هذه النتائج باستخدام (، بينما األصناف التي أظهرت مستويات مختلفة من المقاومة البطيئة عالية، RRI=9) RRI رات تظهر قيمة عالية للـلك أقل قيم للمؤشتاألصناف المحلية والتي تم
والذي تم .5أقل من RRIالتوالي. أما األصناف التي أظهرت أعلى قيم لجميع المؤشرات كانت قيم ، على 7-5و RRI 8-9 ،7-8متوسطة ومنخفضة تراوحت قيم الـدرجة مقاومة جيدة بقيمة عطت أ من االصناف المدروسة ا صنف 44أن ( للنتائج المسجلة في سنتي الدراسة،ACIخالل حساب متوسط معامل العدوى )حسابه من
(RRI=9 ،)143 ( 8-7درجة مقاومة مرغوبة RRI= ،)75 ( 6-5صنف محلي كانت مقاومتها مقبولة RRI= بينما كانت بقية األصناف حساسة إلى شديدة ) الحساسيةوالعالم بمصادر وراثية مقاومة التي ستمكن من حماية القمح الطري من ةسوري. وتمكن نتائج هذه الدراسة من امداد برامج التحسين الوراثي في 5قل من أ RRI مع قيمة
يم و لتقهي مؤشرات يعتمد عليها (FRS)صابة النهائية وشدة اإل CI ، معامل الـAUDPC عدوى الصدأ األصفر لسنوات طويلة. وتشير النتائج أيضا إلى أن معامل الـ .ا وإيجابي ا . هذا وأظهرت النتائج أن اإلرتباط بين جميع المؤشرات كان قوي”r“مقاومة الصدأ البطيئة أكثر من مؤشر معدل اإلصابة
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Received: August 14, 2017; Accepted: April 13, 2018 13/4/2018؛ تاريخ الموافقة على النشر: 14/8/2017تاريخ االستالم: